Conventional ceramic piezo wafers, such as PZT, are often constructed for use in connection with bi-morph or unimorph actuators. To use the piezo wafer as an actuator or possibly as an energy harvesting device, it must be strengthened during manufacture by imparting a compressive prestress thereto. One such means for prestressing a wafer of piezoelectric material in a manner that strengthens it is by bonding the layer of piezoelectric material to a “prestressing layer” using a high temperature polyimide adhesive. The compressive stress in the piezoelectric layer is induced by the difference in coefficient of thermal expansion between the piezoelectric material and both the prestressing layer and the adhesive, both of which have much higher coefficients of thermal expansion than the piezoelectric material.
Another approach to hardening a piezoelectric material involves sandwiching a piezoelectric layer of material between two fiber composite panels that are under tension in at least one direction of their plane during the bonding process. The composite panels are held under tension until the bond cures, at which point they are released and a compressive stress is induced in the piezoelectric material.
Until the present time, certain “smart” materials, such as single crystal PZN-PT or PMN-PT, which are known as single crystal piezo (“SCP”) material, have not been used in connection with actuators and/or energy harvesting devices because of the lack of hardness of these materials. This lack of hardness makes SCP material highly prone to fracturing when the SCP material is placed under tension. However, SCP material would otherwise be ideally suited for actuator and energy harvesting applications because of its very high energy density, which is many times that of conventional piezo material.
It is therefore desired to provide a means for manufacturing an actuator or energy harvesting device incorporating an SCP layer of material which is not prone or susceptible to fracturing when placed in tension. Such a hardened SCP material could then be used in a wide variety of tasks such as aerodynamic flow control and structural energy harvesting applications that would otherwise be impossible because of the tendency of the SCP material to fracture when placed in tension.